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Hyperbolic functions

math Maturity 7-9 Next article →

{

"text": "Hyperbolic functions are mathematical tools that act as analogues to ordinary trigonometric functions. While standard trigonometry describes the properties of a circle, hyperbolic functions describe the properties of a hyperbola.

Circular and hyperbolic angle
Circular and hyperbolic angle

Specifically, they relate to the right half of a unit hyperbola. Just as circular functions use a circular angle, hyperbolic functions use a hyperbolic angle. The magnitude of this hyperbolic angle is defined as the area of its hyperbolic sector.

Hyperbolic functions-2
Hyperbolic functions-2

This connection allows mathematicians to extend the concepts of geometry beyond simple circles.\n\nThe basic hyperbolic functions are hyperbolic sine (sinh) and hyperbolic cosine (cosh).

sinh cosh tanh
sinh cosh tanh

These two functions can be defined using the exponential function, $e^u$. Hyperbolic sine is the odd part of the exponential function, calculated as half the difference between $e^u$ and $e^{-u}$.

Hyperbolic and exponential; sinh
Hyperbolic and exponential; sinh

Hyperbolic cosine is the even part, calculated as the average of $e^u$ and $e^{-u}$.

Hyperbolic and exponential; cosh
Hyperbolic and exponential; cosh

From these two, other functions are derived, including hyperbolic tangent (tanh), hyperbolic cotangent (coth), hyperbolic secant (sech), and hyperbolic cosecant (csch).

csch sech coth
csch sech coth

These functions can also be expressed as solutions to specific differential equations.\n\nIn complex analysis, hyperbolic functions arise when applying sine and cosine to imaginary angles. For example, $\sinh(z)$ is equal to $-i \sin(iz)$. This relationship shows how these functions are deeply connected to circular trigonometry through the imaginary unit $i$.

Complex Sinh
Complex Sinh

The hyperbolic sine and cosine are considered entire functions. This means they are well-behaved throughout the whole complex plane. Consequently, the other derived hyperbolic functions are meromorphic. This term describes functions that are analytic except at certain isolated points called poles. By the Lindemann–Weierstrass theorem, these functions yield transcendental values for any non-zero algebraic argument.\n\nThe history of these functions spans several centuries of mathematical discovery. The first known use of hyperbolic trigonometry is attributed to Gerardus Mercator around 1566. He used it to solve problems related to his map projection. Later, in 1687, Isaac Newton suggested the similarity between circular and hyperbolic sectors in his work, *Principia Mathematica*. In 1757, Vincenzo Riccati formally introduced the term \"hyperbolic functions.\" He used the abbreviations $\text{sin}$ and $\text{cos}$ for circular functions and $\text{sinh}$ and $\text{cosh}$ for hyperbolic ones.

Complex Cosh
Complex Cosh

By the 1760s, Johann Heinrich Lambert systematized these functions and provided their exponential expressions. Lambert is responsible for the specific abbreviations used in modern mathematics.\n\nHyperbolic functions are vital for solving many types of equations in physics and engineering. They appear in the solutions of linear differential equations, such as the equation defining a catenary. A catenary is the specific curve formed by a flexible chain hanging freely under its own weight. They are also used to solve cubic equations and Laplace's equation in Cartesian coordinates. Laplace's equation is a fundamental tool used in electromagnetic theory, heat transfer, and fluid dynamics. Furthermore, they are used to express Lorentz boosts as hyperbolic rotations within the framework of special relativity. They also help express the angle of parallelism in hyperbolic geometry.\n\nOne notable property involves the relationship between the hyperbolic cosine and arc length. The area under the curve of the hyperbolic cosine over a finite interval is always equal to the arc length of that interval. Additionally, the hyperbolic tangent is the unique solution to the differential equation $y' = 1 - y^2$ with the initial condition $y(0) = 0$. There are also many identities that mirror trigonometric identities. Osborn's rule provides a way to convert trigonometric identities into hyperbolic ones. This rule involves expanding the identity and switching the signs of terms containing a product of two hyperbolic sines.\n\nUltimately, hyperbolic functions represent a significant expansion of trigonometry. They allow for the measurement of complex curves and growth patterns that circles cannot describe. They connect the world of exponential growth to the world of geometric shapes. Whether studying the flow of fluids or the behavior of light, these functions provide the necessary language. They bridge the gap between real-valued geometry and the complex plane. This makes them an essential part of the mathematical toolkit for understanding the physical universe.",

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"File:sinh cosh tanh.svg",

"File:Hyperbolic and exponential; sinh.svg",

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🖼️ Images & Media (13)
File:sinh cosh tanh.svg
sinh cosh tanh.svg
File:Hyperbolic functions-2.svg
Hyperbolic functions-2.svg
File:Cartesian_hyperbolic_rhombus.svg
Cartesian_hyperbolic_rhombus.svg
File:Hyperbolic and exponential; sinh.svg
Hyperbolic and exponential; sinh.svg
File:Hyperbolic and exponential; cosh.svg
Hyperbolic and exponential; cosh.svg
File:csch sech coth.svg
csch sech coth.svg
File:Circular and hyperbolic angle.svg
Circular and hyperbolic angle.svg
File:Complex Sinh.jpg
Complex Sinh.jpg
File:Complex Cosh.jpg
Complex Cosh.jpg
File:Complex Tanh.jpg
Complex Tanh.jpg
File:Complex Coth.jpg
Complex Coth.jpg
File:Complex Sech.jpg
Complex Sech.jpg

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